1. Field of the Invention
The present invention relates to a projection image display apparatus using a scan mirror which vibrates in a sine vibration manner.
2. Description of Related Art
Conventionally, there is known a projection image display apparatus using a resonant scan mirror as a projection image display apparatus such as a projector or the like. When the scan mirror is made to vibrate by a sine wave alternating current, the scan rate of the mirror is sinusoidally changed with respect to time.
FIG. 4 shows a relation between scan angle and scan rate of the scan mirror which vibrates in the sine vibration manner. As shown in FIG. 4, the scan rate of the scan mirror reaches maximum at the center of an image where the scan angle (vibration amplitude) is zero and the scan rate of the scan mirror is zero at the edges of the image where the scan angles are maximum values of X and −X in horizontal direction (or, maximum values of Y, −Y in vertical direction). Therefore, scan width per time unit is not constant, and the scan width becomes smaller as approaching the edges of the image. Because the speed of the scan mirror is not constant, problems such that the image to be projected on the screen is distorted and that the brightness of the image is uneven occur.
In view of the above problems, in JP2004-279544, there is suggested an image display apparatus which corrects the equally spaced characteristic of line images in the scanning direction which occurs because of the deflection unit and the scan lens system, that is, an image display apparatus which carries out correction for spaces between each line images on a screen by changing the time interval of pixel clock for each pixel line unit. For example, the pixel clock having a time interval which is longer than the regular clock is mixed in the pixel clock corresponding to the periphery blocks among the blocks in which the scanning area is divided. Thereby, the equally spaced characteristic is to be corrected.
However, the technology for correcting the equally spaced characteristic disclosed in JP2004-279544 is carried out by controlling the time interval of the image clock, and there is a problem that the structure will be complicated because electrical control is needed.